Non-collinear phase

Nanometer scale domain configurations in fe bulk crystals pave the way for a new class of photonic devices. As an example, preliminary calculations show that a uv laser (A = 300 nm) based on second harmonic generation in LiTaC>3 crystal requires a periodic nanodomain superlattice with domain widths of around 700 nm. In addition, the current domain gratings in ferroelectric crystals are suitable only for quasi-phase-matched nonlinear interactions in the forward direction, where the pump and generated beams propagate in the same direction. Sub-micron ferroelectric domain gratings are the basis for a new family of devices based on backward nonlinear quasi-phase-matched optical interactions in which the generated beam travels in a reverse or another non-collinear direction to the incident beam. Non-collinear... 

Figure 10.4 Nanodomain grating (domain period is 410 nm) tailored for integrated optical device in LiNbC>3 crystal by application of dc voltage (U = 2.0kV). (b) Domain grating (domain period is 1180nm) fabricated in the RbTiOPCU crystal for non-collinear quasi-phase-matched nonlinear optical converter.

A3 corresponds to the white line and X2 to the minimum in/ ) and draw the corresponding phasing circles, we get a well-resolved unique phase (figure 9.10). The centres of these phasing circles are well separated and non-collinear this is necessary and sufficient for phasing (as has also been pointed out by Templeton et al (1980b), and by Ramaseshan and Narayan (1981)). 

Figure 9.10 The centres for the phasing circles in this Harker diagram are based on the Friedel equivalent pair at the white line (or just on the short A side of the edge) and one equivalent for the minimum off (i.e. two wavelengths in total). The centres are well separated and non-collinear and the unique phase is well resolved. From Flelliwell (1984) with the permission of the Institute of Physics.

The second volume of Laser Spectroscopy covers the different experimental techniques, necessary for the sensitive detection of small concentrations of atoms or molecules, for Doppler-free spectroscopy, laser-Raman-spectroscopy, doubleresonance techniques, multi-photon spectroscopy, coherent spectroscopy and time-resolved spectroscopy. In these fields the progress of the development of new techniques and improved experimental equipment is remarkable. Many new ideas have enabled spectroscopists to tackle problems which could not be solved before. Examples are the direct measurements of absolute frequencies and phases of optical waves with frequency combs, or time resolution within the attosecond range based on higher harmonics of visible femtosecond lasers. The development of femtosecond non-collinear optical parametric amplifiers (NOPA) has considerably improved time-resolved measurements of fast dynamical processes in excited molecules and has been essential for detailed investigations of important processes, such as the visual process in the retina of the eye or the photosynthesis in chlorophyl molecules. 

The magnetic stractures of TbPdln and DyPdln were solved from powder neutron diffraction data (Javorsky et al., 1998, 2000). TbPdln is a non-collinear k = (0,0,0) ferromagnet with the terbium magnetic moments within the basal plane. For DyPdln two different mag-netie phases are observed. In the high-temperature phase, 15 K < T < Tord, the dysprosium... 

A fourth method for phase matching is the use of non-collinear waves, as shown in Fig. 13. This technique can be used for sum-frequency processes in media with negative dispersion and for difference-frequency processes in media with positive dispersion. It is commonly used, for example, in liquids for the difference frequency process tU4 = 2o) — 0)2. 

A nondirect product basis expansion method described in the previous section on gas-phase reaction, similar to the spirit of L-shaped grid method proposed by Mowrey (91), is also used in gas-surface reactions. This method is actually ideal for gas-surface reaction because the skewing angle of the PES is strictly 90° (see Fig. 14). A collinear model study showed explicitly that the required number of quasiadiabatic diatomic vibrational function is only larger near the potential saddle point region (92). Based on the treatment of non-direct product basis described in the previous section (Eq. 89), the translation basis function is given by... 

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